1. Field of the Invention
The present invention relates to a fuel supply apparatus and a vapor separator in an outboard engine provided with a fuel injection system.
2. Description of Related Art
Conventionally, an engine provided with a fuel injection system is constructed to be supplied with a predetermined amount of fuel by means of an injector placed in an intake passage and an electrically controlled fuel pump and a predetermined amount of air supplied under the control of a throttle valve. A fuel supply apparatus in an outboard engine provided with a fuel tank mounted on a ship's body needs a long pipe for fuel supply to connect the tank to the engine. A vapor separator serving as an auxiliary, tank is therefore disposed near the engine.
An example of the above fuel supply apparatus in the outboard engine is disclosed in Japanese patent unexamined publication No. 2001-140720. This fuel supply apparatus includes a fuel tank, a vapor separator, a high-pressure fuel pump for supplying fuel to an injection nozzle (an injector) of an engine intake system, and an ECM for controlling fuel injection from the injection nozzle. The fuel supply apparatus is constructed to supply fuel to a combustion part (an engine combustion chamber) together with air supplied through the throttle body. The fuel supply apparatus further includes a first fuel vapor hose connected in communication to a reservoir part which stores fuel vapor in the vapor separator, a second fuel vapor hose connected in communication to the intake passage upstream of the throttle body, and a buffer part connected in communication to the first and second fuel vapor hoses and used for buffering the flow of fuel vapor.
In the vapor separator, normally, a float 101 is provided as shown in FIG. 19. This float 101 serves to adjust an amount of fuel to be supplied from a fuel pump 102 in order to maintain a constant amount of fuel in a vapor separator 100. Accordingly, an air layer and a fuel layer are formed in the vapor separator 100. The vapor separator 100 is provided, on the air layer side, with a pipe called a vent port 103 having an open end opening into the vapor separator 100 in order to produce a pressure substantially equal to atmospheric pressure in the vapor separator 100. The other end of the vent port 103 is connected to an intake passage to return fuel vapor generated in the vapor separator 100 to the intake passage. This is because the vapor generated in the vapor separator 100 is combustible, which may cause a fire if released into the atmosphere and cause atmospheric pollution.
However, the vapor separator of the fuel supply apparatus in the outboard engine, including one disclosed in Japanese patent unexamined publication No. 2001-140720, has a disadvantage that a large amount of vapor is generated at high temperature conditions due to heat, vibration, agitation caused by supplied fuel and return fuel, and decompression and boiling of the return fuel, and the vapor would be mixed in the air layer. The vapor separator has been configured to return the generated vapor to the intake passage as mentioned above, so that an air/fuel (A/F) ratio is liable to vary according to the amount of the vapor returned to the intake passage. This would deteriorate engine performances at the high temperature conditions.